When a multilayer ceramic capacitor is used in the vicinity of a CPU for a decoupling application, since an equivalent series resistance (ESR) of the multilayer ceramic capacitor is excessively low, oscillation is generated on a circuit due to parallel resonance, and as a result, the impedance disadvantageously increases. Hence, as for multilayer ceramic capacitors used for the application described above, it has been desired to control the ESR within the range of several tens to several thousands of milliohms. As a technique to satisfy this desire, it has been proposed that a function as a resistance element is also imparted to external electrodes of a multilayer ceramic capacitor.
For example, in International Publication 2006/022258 pamphlet (Patent Document 1), a technique has been disclosed that in a multilayer ceramic capacitor including internal electrodes that contain Ni or a Ni alloy, external electrodes are each formed, for example, to have a two-layer structure in which a resistance electrode containing a glass component and a composite oxide (preferably an In—Sn composite oxide) that reacts with Ni or a Ni alloy is formed as a lower layer and in which a conductive electrode containing, for example, Cu or a Cu alloy as a primary component is formed as an upper layer.
In addition, the Patent Document 1 has disclosed that in order to control the ESR, the glass content and/or the glass softening point of the resistance electrode functioning as the lower layer of the external electrode is changed. In a particular embodiment described in the Patent Document 1, B—Si—Zn—Ba—Ca—Al-based glasses having softening points of approximately 560° C., approximately 580° C., and approximately 600° C. are used.
On the other hand, in the Patent Document 1, the glass contained in the conductive electrode functioning as the upper layer of the external electrode has not been specifically described.
In addition, in Japanese Unexamined Patent Application Publication No. 2004-128328 (Patent Document 2), a technique has been disclosed that in a multilayer ceramic capacitor including internal electrodes that contain Ni or the like, external electrodes are each formed, for example, to have a two-layer structure in which a resistance electrode containing a glass and a conductive material selected from ruthenium oxide, a ruthenium oxide compound, and graphite/carbon is formed as a lower layer, a conductive electrode containing a glass and a conductive material selected, for example, from Cu and Ni is formed as an upper layer, and the glass contained in the upper layer is the same as that contained in the lower layer.
When the multilayer ceramic capacitor as described above is manufactured, the lower layer resistance electrode and the upper layer conductive electrode of the external electrode are each formed by a firing step, and in order to obtain a stable ESR through the firing steps, the flow of glass from the upper layer conductive electrode into the lower layer resistance electrode or the flow of glass toward an interface portion therebetween must be suppressed.
However, for example, when the same glass as that in the lower layer resistance electrode is used in the upper layer conductive electrode, in the firing to form the upper layer conductive electrode, the flow of glass from the upper layer conductive electrode into the lower layer resistance electrode or toward the interface portion therebetween cannot be suppressed, and as a result, the resistance of the lower layer resistance electrode or the resistance of the interface portion may increase in some cases. As a result, the ESR may exceed an ESR value aimed only by the lower layer resistance electrode in some cases, and the control (adjustment) of the aimed ESR value is difficult to perform.
Patent Document 1: International Publication WO pamphlet
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-128328